Add a diagnostic.getServerPort analysis server request.

pkg/analysis_server/test/integration/diagnostic/test_all.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import 'get_diagnostics_test.dart' as get_diagnostics_test;
+import 'get_server_port_test.dart' as get_server_port_test;
 
 main() {
   defineReflectiveSuite(() {
     get_diagnostics_test.main();
+    get_server_port_test.main();
   }, name: 'diagnostics');
 }